1. Field of the Invention
The present invention relates to a distance measuring device disposed in a camera to measure a distance from the camera to a photographed object.
2. Description of the Related Art
Japanese Patent Application Laying Open (KOKAI) No. 60-217321 and Japanese Patent Publication (KOKOKU) No. 1-57891 show an automatic focusing camera for measuring distances between many points. In this automatic focusing camera, a distance measuring means is moved from one end of a photographing screen to the other end thereof so as to easily focus a photographing lens with respect to a photographed object in any position thereof on the photographing screen.
In the above camera, since the distances between many points are measured, it is possible to prevent so-called intermediate defocusing in which the photographing lens is focused with respect to a background of the photographed object when a distance from the camera to the photographed object is measured at only one point. However, when a one-point distance measuring operation is released, the distance measuring means is automatically moved as mentioned above. Accordingly, there is a case in which no focusing operation can be instantly performed with respect to a specified object to be photographed.
To solve this problem, it is considered to construct the distance measuring device such that the distance measuring device performs both the many-point distance measuring operation and the one-point distance measuring operation. However, such a distance measuring device has various kinds of problems.
Namely, it is not necessary to move the distance measuring means in the one-point distance measuring operation. Further, it is necessary to stop the distance measuring means so as to perform the distance measuring operation, and a focusing lock is required. In the many-point distance measuring operation, it is necessary to move the distance measuring means and no focusing lock is required. Accordingly, the distance measuring device must have a structure corresponding to these distance measuring operations.
When a focusing lock function is added to the camera in the general many-point distance measuring operation, a driving sound is generated by the operation of a mechanical system when the distance measuring means is moved. This driving sound is generated when a first releasing operation of the camera is started. Therefore, an operator of the camera misunderstands that a shutter of the camera is released. Accordingly, there is a problem that the shutter of the camera cannot be reliably released in a certain case.
Further, in the above automatic focusing camera, a resetting operation of the camera with respect to the movement of the distance measuring means in a distance measuring range thereof is performed in association with the winding-up operation of a film in the camera. When a multiple exposure operation is performed, the above resetting operation must be performed irrespective of the winding-up operation of the film. Accordingly, it is impossible to cope with such a situation in the case of the above automatic focusing camera.
There is a distance measuring method of a light-emitting type in which light emitted from a light-emitting element is received by a light-receiving element to perform a distance measuring operation. In this distance measuring method, the distance measuring operation is performed many times at one point to improve an accuracy in distance measurement. An average value of these measured results is used to determine the distance between the camera and the photographed object. A time of several ten milliseconds per one point is normally required in such multiple light emission. Therefore, it is necessary to make a distance measuring optical system at rest in the course of this light emission. However, the above automatic focusing camera has a problem about reliability in data since the distance measuring optical system is continuously moved.